Effects of labile carbon on anaerobic decomposition processes in permafrost wetlands

2021 ◽  
Author(s):  
Maija E. Marushchak ◽  
Hannu Nykänen ◽  
Jukka Pumpanen ◽  
A. Britta K. Sannel ◽  
Lena Ström ◽  
...  
Keyword(s):  
Active Layer ◽  
Soil Incubation ◽  
Labile Carbon ◽  
Soil Layers ◽  
Anaerobic Decomposition ◽  
Permafrost Thaw ◽  
Ground Collapse ◽  
Decomposition Processes ◽  
Arctic Wetlands

<p>Climate warming and permafrost thaw are exposing the large carbon (C) pools of northern wetlands to enhanced decomposition, potentially increasing the release of the greenhouse gases carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>). Permafrost thaw is usually associated with changes in hydrology and vegetation: Ground collapse leads to the formation of new, productive thermokarst wetlands, and active layer deepening allows plant roots to penetrate to deeper soil layers. These processes promote interaction between old permafrost carbon and recent plant-derived carbon, but the effect of this interaction on anaerobic decomposition processes is poorly known.</p><p>Here, we report the preliminary results of a 1+-year-long soil incubation experiment where we investigated the role of fresh organics on anaerobic decomposition in arctic wetlands. We sampled mineral subsoil of Greenlandic wetland sites and the active layer and permafrost peat in a Swedish palsa mire, and incubated them with and without repeated amendments of <sup>13</sup>C enriched glucose and cellulose. We determined the rate and isotopic composition of CO<sub>2</sub> and CH<sub>4</sub> with an isotopic laser, and estimated the contribution of soil organic matter decomposition vs. added carbon to the total C gas release. These results represent new understanding on how plant-derived organics change the magnitude and composition of C gas, thus affecting the climatic feedbacks from permafrost wetland C pool.</p>

The role of rainfall in the thermal-moisture dynamics of the active layer at Beiluhe of Qinghai-Tibetan plateau

2013 ◽  
Vol 71 (3) ◽  
pp. 1195-1204 ◽  
Author(s):  
Zhi Wen ◽  
Fujun Niu ◽  
Qihao Yu ◽  
Dayan Wang ◽  
Wenjie Feng ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Active Layer ◽  
Moisture Dynamics

scholarly journals Unearthing the Boreal Soil Resistome Associated with Permafrost Thaw

2020 ◽  
Author(s):  
Tracie J. Haan ◽  
Devin M. Drown
Keyword(s):  
Antibiotic Resistance ◽  
Active Layer ◽  
Resistance Genes ◽  
Soil Bacteria ◽  
Bacterial Community Composition ◽  
Ecological Niches ◽  
Whole Genome ◽  
Near Surface ◽  
Permafrost Thaw ◽  
Insight Into

ABSTRACTUnderstanding the distribution and mobility of antibiotic resistance genes (ARGs) in soil bacteria from diverse ecological niches is critical in assessing their impacts on the global spread of antibiotic resistance. In permafrost associated soils, climate and human driven forces augment near-surface thaw altering the overlying active layer. Physiochemical changes shift bacterial community composition and metabolic functioning, however, it is unknown if permafrost thaw will affect ARGs comprising the boreal soil resistome. To assess how thaw shifts the resistome, we performed susceptibility testing and whole genome sequencing on soil isolates from a disturbance-induced thaw gradient in Interior Alaska. We found resistance was widespread in the Alaskan isolates, with 87% of the 90 isolates resistant to at least one of the five antibiotics. We also observed positive trends in both the proportion of resistant isolates and the abundance of ARGs with permafrost thaw. However, the number of ARGs per genome and types of genes present were shown to cluster more strongly by bacterial taxa rather than thaw emphasizing the evolutionary origins of resistance and the role vertical gene transfer has in shaping the predominantly chromosomally encoded ARGs. The observed higher proportion of plasmid-borne and distinct ARGs in our isolates compared to RefSoil+ suggests local conditions affect the composition of the resistome along with selection for ARG mobility. Overall taxonomy and geography shape the resistome, suggesting that as microbial communities shift in response to permafrost thaw so will the ARGs in the boreal active layer.IMPORTANCEAs antibiotic resistance continues to emerge and rapidly spread in clinical settings, it is imperative to generate studies that build insight into the ecology of environmental resistance genes that pose a threat to human health. This study provides insight into the occurrence of diverse ARGs found in Alaskan soil bacteria which is suggestive of the potential to compromise health. The observed differences in ARG abundance with increasing permafrost thaw suggest the role of soil disturbance in driving the distribution of resistant determinants and the predominant taxa that shape the resistome. Moreover, the high-quality whole genome assemblies generated in this study are an extensive resource for microbial researchers interested in permafrost thaw and will provide a steppingstone for future research into ARG mobility and transmission risks.

Photocatalytic NOx abatement: The role of the material supporting the TiO2 active layer

2012 ◽  
Vol 211-212 ◽  
pp. 203-207 ◽  
Author(s):  
Claudia L. Bianchi ◽  
Carlo Pirola ◽  
Elena Selli ◽  
Serena Biella
Keyword(s):  
Active Layer ◽  
Nox Abatement

The Role of Dissolved CH4 in Soil Solution in the CH4 Emission from Water-Saving Irrigated Rice Fields

2011 ◽  
Vol 148-149 ◽  
pp. 977-982
Author(s):  
Dao Xi Li
Keyword(s):  
Soil Solution ◽  
Early Stage ◽  
Dominant Role ◽  
Water Layer ◽  
Water Saving ◽  
Rice Fields ◽  
Chromatography Method ◽  
Soil Layers ◽  
Soil Solutions

To examine how the dissolved CH4 in soil solution would affect the CH4 emission from rice field, fluxes of CH4 emission were measured by using a manually closed static chamber-gas chromatography method, and the dissolved CH4 in soil solution was obtained through shaking soil solutions, which were extracted from different paddy soil layers by a soil solution sampler with suction and pressure. The results show that the CH4 fluxes from rice fields and the concentration of dissolved CH4 in soil solution are both reduced significantly under the water-saving irrigation as compared to the traditional flooded irrigation. Under the water-saving irrigation, naturally receding water-layer during the early stage leads to an earlier peak of CH4 flux, but dramatically reduces the concentration of dissolved CH4 in soil solution. The maximum concentration is shifted to about 20-cm depth soil layers, and the relationship between CH4 emissions and dissolved CH4 in soil solution can be estimated using an exponential function of dissolved CH4 in soil solution at the depth of about 20 cm (R2＝0.89, p4 in soil solution plays a more dominant role in CH4 emission under the water-saving irrigation than that under continuously flooded irrigation.

The role of N transformations in the formation of acidic subsurface layers in stock urine patches

Soil Research ◽  
2004 ◽  
Vol 42 (2) ◽  
pp. 221 ◽  
Author(s):  
J. R. Condon ◽  
A. S. Black ◽  
M. K. Conyers
Keyword(s):  
Soil Surface ◽  
Urea Hydrolysis ◽  
Balance Model ◽  
Urea Solution ◽  
Nitrogen Transformations ◽  
N Transformations ◽  
Soil Layers ◽  
Subsurface Layers ◽  
Dominant Process

This study examines the role of nitrogen transformations in the acidification of soil under stock urine patches, specifically the formation of acidic subsurface layers. These are horizontal planes of acidity several centimetres below the soil surface. Glasshouse studies were conducted to relate nitrogen transformations to measured pH changes in soil treated with urine or urea solution (simulated urine). Acidic subsurface layers formed in both urine- and simulated urine-treated soil. With the development of a H+ balance model, the contribution of nitrogen transformations to changes in the H+ concentrations in simulated urine patches was determined.During the first 9 days following treatment, urea hydrolysis and NH3 volatilisation dominated changes in H+ concentration. After that, net immobilisation contributed to H+ changes; however, nitrification was the dominant process occurring. Downward movement of NH4+ originating from urea hydrolysis allowed more nitrification to occur in lower soil layers. The net result of these processes was net acidification of the 4–6, 6–8, and 8–10 cm layers by approximately 0.7, 0.6, and 0.3 pH units, respectively. Thus nitrogen transformations were responsible for the formation of acidic subsurface layers in simulated stock urine patches within 6 weeks of application.

Roles of clay layers in rainfall-runoff processes in a serpentinite headwater catchment

2020 ◽  
Author(s):  
Takahiko Yoshino ◽  
Shin'ya Katsura
Keyword(s):  
Water Flow ◽  
Groundwater Level ◽  
Mineral Soil ◽  
High Water ◽  
Organic Soil ◽  
Rainfall Runoff ◽  
Soil Layers ◽  
Clay Layers ◽  
Headwater Catchment

<p>Rainfall-runoff processes in a headwater catchment have been typically explained by water flow in permeable soil layers (comprised of organic soil layers and mineral soil layers produced by weathering of bedrock) overlying less permeable layers (i.e., bedrock). In a catchment where mineral soils are characterized by clayey materials (e.g., mudstone, slate, and serpentine catchment), it is possible that mineral soil layers function substantially as less permeable layers because of a low permeability of clayey materials. However, roles of clay layers in rainfall-runoff processes in such a headwater catchment are not fully understood. In this study, we conducted detailed hydrological, hydrochemical, and thermal observations in a serpentinite headwater catchment (2.12 ha) in Hokkaido, Northern Japan, where mineral soil layers consisting of thick clay layers (thickness: approximately 1.5 m) produced by weathering of the serpentinite bedrock underlies organic soil layers (thickness: approximately 0.4 m). Saturated hydraulic conductivity (Ks) and water retention curve of these two layers were also measured in a laboratory. The observation results demonstrated that groundwater was formed perennially in the organic soil layers and clay layers. The groundwater level within the organic soil layers and specific discharge of the catchment showed rapid and flashy change in response to rainfall. In contrast, the groundwater level within the clay layers showed slow and small change. Temperature of the groundwater and stream water suggested that water from the depth of the organic soil layers contributed to streamflow. The electric conductivity (EC) of the groundwater in the clay layers was very high, ranging from 321 to 380 µS cmˉ¹. On the other hand, the EC of soil water (unsaturated water stored in the organic soil layers) was relatively low, ranging from 98 to 214 µS cmˉ¹. Hydrograph separation using EC showed that contribution of water emerging from the clay layers to the total streamflow ranged from 31 to 76% in low to high flow periods. Temporal variation in the total head, measured using tensiometers installed at four depths at the ridge of the catchment, indicated that in wet periods when the groundwater level in the organic soil layers was high, water flow from the organic soil layers to the clay layers occurred, whereas, in dry periods, water flow from the clay layers into the organic soil layers occurred. The laboratory measurements showed that the organic soil layers had high Ks (10ˉ² cm sˉ¹) and low water-holding capacity, whereas the clay layers had low Ks (10ˉ⁴ cm sˉ¹) and high water-holding capacity. It can be concluded from these results that clay layers play two roles: (1) forming perched groundwater table and lateral flow on the clay layers (the role of less permeable layers) and (2) supplying water into the organic soil layers in the dry periods (the role of water supplier).</p>

Modeling of soil carbon dynamics, with focus on microbial activity

2020 ◽  
Author(s):  
Elin Ristorp Aas ◽  
Terje Koren Berntsen ◽  
Alexander Eiler ◽  
Helge Hellevang
Keyword(s):  
Organic Matter ◽  
Soil Carbon ◽  
Mycorrhizal Fungi ◽  
Carbon Dynamics ◽  
Carbon Pools ◽  
Soil Processes ◽  
Soil Carbon Dynamics ◽  
Decomposition Processes ◽  
A Site

<p>The representation of soil carbon dynamics is a major source of uncertainty in Earth System Models (ESMs). The terrestrial carbon pool is more than twice the size of the atmospheric pool. Therefore, the role of soil carbon as a source or a sink of atmospheric carbon, and in feedback loops is important to quantify in a changing climate. Decomposition processes of organic matter in soil have often been represented by first order decay equations, which make comparison and validation against observations difficult. Therefore, quantification of the uncertainties  and validation of improved parameterizations are problematic. An emerging approach to tackle these challenges is to represent microbial soil processes explicitly in the models. Following this approach, we have built a process based module that represent the carbon fluxes during soil decomposition, from aboveground litter to soil organic matter (SOM). The role of saprotrophs and mycorrhizal fungi is explicitly represented with separate carbon pools with associated fluxes. On a site level, we compare initial results from the stand alone module with both existing models and observations of carbon pools and fluxes. The observations are from the Norwegian Dovre Mountains, with data from three different alpine communities. These geographic areas are important, because they are subject to changes due to shrubification. In addition, these ecosystems can store large amounts of carbon. By modeling these sites, we gain more insight in the most important processes in soil decomposition, and how different microbial communities affect the carbon dynamics. We will further refine the module by expanding our study with more sites. The long-term objective is to develop an improved module that can be used to represent soil processes in ESMs, and thereby reduce the uncertainty connected to the exchange of carbon between land and atmosphere.</p>

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